This invention relates to a controller in which a computer is incorporated, and particularly to a controller to which specific and variable programs can be supplied by an operator.
For example, a controller having a microcomputer incorporated therein is used to execute by the combination of some computing elements in accordance with the function of the controller, a process control such as a PID control loop with upper and lower limit alarm, and a gas flow control loop with temperature and pressure compensation ability. In order to combine computing elements, a computing program is necessary, and the controller is constructed to specify and change a desired computing program by key operation.
In this conventional controller, however, the computing elements include: Control computing elements such as a standard PID control computing element, a nonlinear PID control computing element, and a linear control computing element; and general computing elements such as computing elements of addition, subtraction, multiplication and division, an absolute value computing element and a square root computing element; the total number of which amounts to several tens of different kinds of computing elements. In addition, the computing program necessary for forming a control loop by selecting proper ones from such a large number of computing elements is produced by normally using assembly language or compiler language. Such a program language can easily be employed by those skilled in the software field of computer technology, but is difficult to use for the actual operators of the controller. Therefore, much labor is required for modification and any change of the program in the field of process control.